Manihot carthagenensis (Tapioca, Cassava) - A unusual looking upright perennial woody deciduous shrub with tuberous roots that can reach to 15 feet in the tropics but is more typically 8 to 12 feet tall here in California. It has attractively dissected palmately-compound dark green leaves on long reddish petioles that are 6 to 8 inches wide on a petiole of about the same length. It has terminal clusters of pale green to yellow-brown non showy flowers in summer which are followed by green round seed pods that open explosively to spread its seeds around the garden – this reseeding can be somewhat of a nuisance but the seedings are easy to remove and do not spread into non irrigated areas. Plant in part sun to light shade (will tolerate full sun along the coast) in any soil (tolerates poor soils) and irrigate only occasionally to very little. It is a drought tolerant plant that can be found in dry neglected sites in frost free areas of Santa Barbara but if one is cultivating the plant for its tubers then more irrigation would benefit the plant. Although considered root hardy to USDA Zone 8 (10 F) the stems will freeze to the ground as temperatures drop much below 25 F and usually it is deciduous in winter, dying back to the main woody stems – can be cut back to the harder wood in late fall or early winter to keep the plant looking neat. This plant has an incredible natural range from dry coastal shrub forests on limestone soils from southern Texas to Brasil . The name for the genus comes from the Brazilian name 'manioc' which was used for cassava and the specific name comes from the collection locale of Cartagena, an area of Bolivia and Columbia. We have long listed this plant erroneously as Manihot esculenta, which is the tropical Tapioca plant which we cannot actually grow in our climate. We thank Geoff Stein for pointing out this error and for speculating that the plant was actually Manihot grahamii. There is certainly considerable confusion about these species but we believe the plant that we actually grow is the hardier Manihot carthagenensis. This is how this plant is identified also in Robert Mulller and Robert Haller's The Trees of Santa Barbara (Santa Barbara Botanic Garden, 2005) and by Peter Riedel in his Plants for Extra-tropical Regions published after his death in 1957 where he notes that Manihot carthagenensis was first introduced into the Santa Barbara area in the 1920's. Our plants originally from Franceschi Park in Santa Barbara. There is disagreement about the spelling of the specific epithet with The Plant List spelling it "carthaginensis" while MOBOT in their Tropicos listing noting that "The correct orthography of the epithet is "carthagenensis" as originally published, ICBN Art. 60.1 (frequently mistakenly cited as "carthaginensis")".
This description is based on our research and observations made of this plant as it grows in our nursery, in the nursery garden and in other gardens that we have visited. We will also incorporate comments received from others and always appreciate getting feedback of any kind from those who have some additional information about this plant, in particular if this information is contrary to what we have written or if they have additional cultural tips that would aid others in growing Manihot carthagenensis.